1. Field of the Invention
The present invention relates to a method and an apparatus for manufacture of a cathode-ray tube, and more particularly to an apparatus and method concerned with an electron gun heating technique required during evacuation of a tube body in the process of manufacturing a cathode-ray tube.
2. Description of the Prior Art
In manufacture of a cathode-ray tube, it is necessary to evacuate the same to a high vacuum degree. Therefore, as disclosed in Japanese Utility model Publication No. 61 (1986)-15585 for example, an electron gun is heated to a high temperature in the process of evacuating the tube body so that the entire complement of electrodes of the electron gun are degassed with positive removal of any extraneous substances therefrom to consequently achieve complete evacuation.
For the purpose of further raising the vacuum degree in the tube after such gun heating step, it is customary to flash a getter material by heating a getter container so as to adsorb any residual gases in the tube body.
In evacuating a cathode-ray tube during the manufacture thereof as illustrated in FIG. 1, an electron gun 2 is disposed in a neck portion of a tube body 1 of the cathode-ray tube. In the electron gun 2, for example, three cathodes Kl, K2, K3 for emitting three electron beams therefrom are arranged on a horizontal line as viewed from a fluorescent screen (not shown) provided on the front of the cathode-ray tube or opposite to the electron gun 2. Cup-shaped grid electrodes G11, G12, G13 of a first grid electrode G1 are disposed respectively opposite to the discrete cathodes K1, K2, K3. Meanwhile a second grid electrode G2, a third grid electrode G3, a fourth grid electrode G4 and a fifth grid electrode G5 are arranged in common to the grid electrodes G11, G12, G13 concentrically with the center cathode K2 and the first grid electrode G12. And in a stage posterior to the fifth grid G5, a convergence means C is disposed for converging the three electron beams from the cathodes K1, K2, K3 onto the fluorescent screen. A getter container 4 is provided at the fore end of the convergence means C, which is located in front of the electron gun 2, via a spring 3 in such a manner as to be positioned outside the paths of electron beams. On the inner surface of a funnel portion of the tube body 1, there is deposited an internal conductor film 5 to which a high voltage (anode voltage) is applied, and free ends of a plurality of conductive springs 6 provided at the distal end of the electron gun 2 are arranged around the axis of the electron gun 2 and are resiliently kept in contact with the conductor film 5. The high voltage applied via such conductive springs 6 to the internal conductor film 5 is supplied as a fixed voltage to both the first grid electrode G5 and the third grid electrode G3 connected electrically thereto, and also to the convergence means C. The electron gun 2 is disposed concentrically with the axis of the neck portion of the tube body 1 by means of such conductive springs 6.
Denoted by 7 is a beading glass member for holding the individual electrodes in a predetermined positional relationship to one another. More specifically, the discrete electrodes G11, G12, G13 of the first grid electrode G1 are mechanically interconnected, although not shown, and are held in a predetermined positional relationship to the other electrode, i.e., the second grid electrode G2 by the beading glass member 7. The electron gun 2 has a stem 8 welded to an end of the neck portion of the tube body 1, and lead pins for the electrodes, other than those to which the aforementioned high voltage is applied, are connected to a plurality of terminal pins 9 so provided as to pierce through the stem 8, whereby such other electrodes are electrically energized while being mechanically retained by cooperation with the conductive springs 6.
Evacuation of the tube body 1 is executed via a chip-off pipe 10 so provided as to pierce through the stem 8, and after completion of the evacuation, the pipe 10 is made molten and chipped off by the application of heat thereto to consequently seal up the tube body 1.
For such evacuation, a heating means 11 consisting of a high-frequency induction heating coil is disposed opposite to the periphery of the electron gun 2 as illustrated in FIG. 1, and a high-frequency voltage in a frequency range of 350 to 400 kHz is applied to the heating means 11 so that an induced current is caused to flow in each electrode of the electron gun 2, thereby heating the electrodes. In this case, when heating is executed at a required temperature with regard to the electrodes provided in common to the cathodes K1, K2, K3, i.e., the second through fifth grids G2-G5 within a temperature range of 700.degree. to 750.degree. C. adequate for effectively degassing such electrodes, then the small-diameter grids G11, G12, G13 provided individually with respect to the cathodes K1, K2, K3 fail to be sufficiently heated as the temperature thereof is 600.degree. C. or so, and therefore complete degassing is not achieved. Meanwhile, if the condition is such that the small-diameter grids G11, G12, G13 are heated at a required temperature ranging from 700.degree. to 750.degree. C. for example, then the other electrodes G2-G5 are heated excessively beyond the limit to raise a problem of metal evaporation. Therefore it is customary to carry out the gun heating step in such a manner that the large-diameter common electrodes are heated up to a predetermined temperature of 700.degree. to 750.degree. C. And thereafter the pipe 10 is chipped off to seal up the tube body. Posterior to such evacuation and seal-up, the getter container 4 is similarly heated by the high-frequency induction heating means to execute the getter flashing step as mentioned already, and then the aging step is executed to maintain emission of thermoelectrons from the cathodes of the cathode-ray tube.
However, according to the method described above, the discrete electrodes G11, G12, G13 provided individually to the electron beams are not heated sufficiently, so that complete stabilization is not attainable by the subsequent aging step to eventually bring about characteristic variation, hence causing an impediment to a long service life of the product.
In case the electrodes G11, G12, G13 are provided individually with respect to the electron beams as mentioned, tiny-diameter holes for passing the electron beams therethrough are formed in the electrodes respectively, so that during the operation, impingement of the electrons from the cathodes K1, K2, K3 is great upon the electrodes G11, G12, G13. Therefore, incomplete degassing with regard to the electrodes G11, G12, G13 exerts considerably harmful influence on the desired stable operation and long service life. Furthermore, after the cathode-ray tube is sealed up, the aging is executed as described above to keep emission of thermoelectrons from the cathodes for attaining activation and stabilization of the tube. Degassing the electrons is effected to a certain extent also by the impingement of the electrons emitted in the aging step, and the gases thus removed are adsorbed into the flashed getter material to attain a stabilized state. However, since the beam passage holes formed in the electrodes G11, G12, G13 are tiny in diameter, sufficient degassing is not achieved during the normal aging time. Therefore, the residual gases are released in the operation of the cathode-ray tube after completion as a product to consequently bring about some disadvantages relative to deterioration of the thermoelectron emission characteristics of the cathodes inclusive of slumping and failure in proper emission conforming with cutoff, hence shortening the service life of the cathode-ray tube as a result.